Composite materials having long-range order exist in nature. Natural composites, such as seashells, exhibit extraordinary mechanical properties that stem from the unique hierarchically-ordered structure in these materials. This realization has consequently triggered an effort to mimic nature by building long-range ordered structures at the nanoscale level. Order on the nanoscale can be used in turn to create hierarchically-ordered structures on micron and millimeter scales.
The technology to produce nanoscale inorganic ordered structures includes “top-down” approaches, such as sequential deposition and nanolithography, and “bottom-up” approaches, such as self-assembly based on ionic and nonionic surfactants and block copolymers. Inorganic ceramic materials, such as silica and oxides having nanoscale order, have been obtained by self-assembly using organic species as structure-directing agents. Polymeric precursors have been used to develop nanotubes and nanofibers of boron nitride, boron carbide, and silicon carbide, and to fabricate high temperature micro-electromechanical systems (MEMS) with dimensions in the micron to sub-millimeter range. Block co-polymers have been used to fabricate nanostructured arrays of carbon.
Self-assembly of inorganic precursors by way of block co-polymers or surfactants is emerging as a powerful technique to build nanoscale structures in ceramics materials. Due to excellent control of dispersity in molecular weight of block co-polymers, some of the structures built therefrom possess long-range order. Current technologies along this line use organic block co-polymers. A certain ceramic precursor additive is miscible with one block in the block co-polymer, therefore when in co-existence with the block co-polymer, the precursor additive selectively targets that particular block (phase targeting). The block co-polymer can self-assemble into various structures, with the morphology and size scale determined by molecular weight and its polydispersity, volume fraction between blocks, and processing conditions. Due to this self-assembly and phase targeting of the ceramic precursor additive, structures comprising the precursor additive can thus be realized. When the self-assembled mixture of block co-polymer and precursor additives is heated to high temperatures, the block co-polymer decomposes, and the precursor additives are converted to ceramics, with nanoscale structure (nanostructure) inherited from the block co-polymer/precursor additive hybrid (see U.S. Pat. No. 7,056,849 B2).
The above-described process, however, has areas which can be improved upon, such the effectiveness of phase targeting. Functionalization of the ceramic precursor additives is needed in order to achieve phase selectivity. In most cases, the solubility of the precursor additives in a block is limited, even after functionalization. Furthermore, the organic block co-polymer in the above-described process serves as a structure-directing template, and it is a sacrificial component that needs to be removed during ceramization. The removal of the block co-polymer template causes low overall ceramic yield, adds to the problems of volume shrinkage and gas evolution during the pyrolysis process.
As a result of the forgoing, an alternative method of generating such nanoscale ordered high-temperature ceramics would be desirable—particularly wherein such an alternative method is capable of overcoming the above-described yield and gas evolution limitations.